1. Field of the Invention
The present invention relates generally to an optical pickup device and method of adjusting the same, which is suitably used in various recording apparatuses having a function of recording information in optical information recording media, such as digital versatile discs, etc.
2. Description of the Prior Art
Recently, in order to satisfy requirements for recording/reproducing large quantities of information, an optical disc (optical information recording medium) with memory capacity of more than 20 GB is proposed and utilized. An optical pickup device used to record/reproduce information in the optical disc is problematic in that it requires high Numerical Aperture (NA) of a lens to record/reproduce information of high density, and allowable variation of a thickness of the optical disc becomes narrow.
Therefore, in order to correct variances, such as the irregularity of thickness of the optical disc, etc., an optical pickup device using a beam expander is used. (reference document: Japanese Applied Magnetics Society 113th symposium report pp. 85-91, January 2000, by ICHIMURA Isao and KASAMI Utaka).
FIG. 8 is a view showing the construction of a conventional optical pickup device using a beam expander, wherein a Knife Edge method is applied. Referring to FIG. 8, reference numeral 1 designates a semiconductor laser (LD: light emitting device) to emit blue light, for example, with a wavelength of 400 nm, reference numeral 2 a collimate lens, reference numeral 3 a beam shaping prism in which a pair of prisms are arranged in opposite directions, reference numeral 4 a xcex/2 plate, reference numeral 5 a diffraction grating, reference numeral 6 a polarizing beam splitter, reference numeral 7 a xcex/4 plate, reference numeral 8 a beam expander comprised of two lenses, reference numeral 9 an object lens comprised of two pairs of optical parts, reference numeral 10 a knife edge, reference numeral 11 a photo diode (PD: light receiving device) for a monitor, reference numeral 12 a photo diode (PD) for a servo, reference numeral 13 a photo diode (PD) for RF and servo, and reference numeral 14 an optical disc.
In the optical pickup device, irregularity of thickness of the optical disc 14 is adjusted by varying a distance between two lenses constituting the beam expander 8.
However, the conventional optical pickup device using a beam expander is problematic in that it must adjust the distance between two lenses of the corresponding beam expander 8 to cope with the irregularity of thickness of the optical disc 14 (disc thickness variation). Accordingly, it is required to combine an adjustment tool of the beam expander 8 with the optical pickup device, the size of the entire optical pickup device is increased, and the manufacturing cost thereof is also increased.
Further, the number of lenses used in the entire optical pickup device is increased, thus requiring an additional process of adjusting an optical axis, and increasing the manufacturing cost of the optical pickup device.
Further, the conventional optical pickup device using a beam expander is problematic in that it allows deviation in positions of optical parts, such as lenses, due to secular changes in temperature and humidity in use environment, so operations of adjusting the positions of the optical parts and adjusting the optical axis are required.
Meanwhile, an emission wavelength of the semiconductor laser is dispersed to cause aberrations. However, it is difficult to correct such aberrations.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an optical pickup device and method of adjusting the same, which can correct aberrations due to variation of thickness of an optical disc and the dispersion of an emission wavelength by a semiconductor laser, being generated in manufacturing processes of the optical disc and the optical pickup device, correct aberrations generated in recording/reproducing of the optical disc due to variation of the emission wavelength and secular changes in the environment of the semiconductor laser, simplify and miniaturize the construction of the optical pickup device, and easily reduce the manufacturing cost thereof.
In order to accomplish the above object, the present invention provides an optical pickup device and method of adjusting the same.
In accordance with a first aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device, comprising a light emitting device; a lens system for narrowing light emitted from the light emitting device to a predetermined diameter and condensing the narrowed light onto an optical information recording medium; a light receiving device for detecting light reflected and returned from the optical information recording medium; and a second lens disposed between the light emitting device and the lens system for correcting wavefront aberrations and/or remaining wavefront aberrations, the second lens being fixable at an arbitrary position on an optical axis while moving along the optical axis.
The optical pickup device of the present invention can easily correct remaining wavefront aberrations generated in a manufacturing process of the light emitting device due to dispersion of an emission wavelength caused by the light emitting device itself and tolerance of specifications of other optical parts, by disposing the second lens for correcting wavefront aberrations and/or remaining wavefront aberrations between the light emitting device and the lens system, and allowing the second lens to be fixable at an arbitrary position on an optical axis while moving the second lens along the optical axis.
Further, the present invention can easily correct wavefront aberrations generated due to variation of an emission wavelength by the light emitting device and secular change in the environment of the light emitting device.
Moreover, the present invention can simplify the construction of the optical pickup device, realize miniaturization thereof and reduce manufacturing cost thereof by using a construction allowing the second lens to move.
In accordance with a second aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction and further comprising a liquid crystal optical device disposed between the light emitting device and the lens system, or within the lens system, for correcting wavefront aberration.
In accordance with a third aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction of the first or second aspect of the present invention, wherein the lens system includes a third lens for converting the light emitted from the light emitting device into parallel light, and a fourth lens for narrowing the parallel light from the third lens to a predetermined diameter.
In accordance with a fourth aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction of the third aspect of the present invention and further comprising a lens holder to which the fourth lens and the liquid crystal optical device are mounted opposite each other, the lens holder being shakably supported by a plurality of wires.
The optical pickup device of the present invention can reduce deviation of an axis of the liquid crystal optical device and the fourth lens, and increase accuracy of correction of wavefront aberrations by using a construction in which the fourth lens and the liquid crystal optical device are mounted to the lens holder to be opposite each other, and the lens holder is shakably supported by a plurality of wires.
In accordance with a fifth aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction of the fourth aspect of the present invention, wherein the fourth lens and the liquid crystal optical device are arranged such that their centers are positioned near a driving center of the lens holder.
The optical pickup device of the present invention can maintain weight balance of the fourth lens and the liquid crystal optical device satisfactorily, and does not need an additional heavy balancer by arranging the fourth lens and the liquid crystal optical device such that their centers are positioned near a driving center of the lens holder. Therefore, the optical pickup device of the present invention can easily realize its miniaturization and reduction of its manufacturing cost.
In accordance with a sixth aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction of the fourth or fifth aspect of the present invention, wherein the liquid crystal optical device is designed such that the number of its control terminals is equal to or less than that of the wires and it is electrically controlled through the wires.
The optical pickup device of the present invention can electrically control the liquid crystal optical device through a plurality of wires, does not need additional signal lines for controlling the liquid crystal optical device, and can reduce undesirable effects, such as natural vibration of a driving means like an actuator, generated due to the signal lines for controlling the liquid crystal optical device.
In accordance with a seventh aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device having the above construction of any of the fourth to sixth aspect of the present and further comprising moving magnet-type driving means mounted to the lens holder.
In accordance with an eighth aspect of the present invention, the above object can be accomplished by the provision of an optical pickup device, the optical pickup device comprising a light emitting device, a lens system for narrowing light emitted from the light emitting device to a predetermined diameter and condensing the narrowed light onto an optical information recording medium, a light receiving device for detecting light reflected and returned from the optical information recording medium, and a second lens disposed between the light emitting device and the lens system for correcting wavefront aberrations/or remaining wavefront aberrations, comprising the step of a position of the second lens on the basis of at least one of various pieces of information about one or more parts constituting the light emitting device, the lens system and the light receiving device, about quality of recorded/reproduced information of the optical information recording media as a reference, and about quality of information in recording/reproducing of the optical information recording media.
The optical pickup device adjustment method can easily correct any of remaining wavefront aberrations generated in a manufacturing process of the optical pickup device due to dispersion of an emission wavelength caused by the light emitting device itself and tolerance of specifications of other optical parts, and wavefront aberrations generated due to variation of the emission wavelength by the light emitting device and secular changes in the environment.